This invention, which is the work of Mr. Jean-Pierre MOREAU of CHANTIERS FRANCE-DUNKERQUE and Messrs Pierre LEMERCIER, Henri LIGOZAT, Paul MARCHAL and Jean VERTU of the COMMISSARIAT A L'ENERGIE ATOMIQUE, relates to a submarine vehicle for dredging and raising minerals resting on the sea bed at great depths.
The dredging of minerals and in particular of polymetallic nodules and raising them to the surface from a great depth are generally carried out using two separate machines: on the one hand, the dredging machine, generally placed at the bottom of a long duct, and a hydraulic apparatus for raising the minerals collected in the duct to a surface support.
A process is known using collecting and raising machines. These machines are rendered heavy in relation to the ambient marine medium by the very great compression of gas in their ballasts, whilst the rest of the weight of the structures is compensated by known buoyancy products resistant to high pressure, which are required for the time spent at great depths. When the machine approaches the sea bed, the release of pressure of the gas contained in the ballast simultaneously provides the energy required for collection and for the travel of the vehicle on the sea bed. This pressure release at the end of the operation produces a lightening of the vehicle, thus enabling it to rise to the surface again.
This submarine vehicle for dredging and raising nodules, powered by pneumatic energy, cannot readily be guided during its descent or during its movement on the sea bed. Moreover, the pneumatic energy stored in these dredging machines is required both for the dredging itself and for raising the materials collected from the sea bed and the energy yield is very poor.
French patent application No. 77 01288, filed in the name of the Applicant on Jan. 18th 1977, (U.S. Pat. No. 4,231,171) describes another process wherein the energy required for the accurate manoeuvring of the vehicle and for dredging on the sea bed is stored in the machines in a known form, e.g. in the form of electricity, but the energy required for the descent and re-ascent of the vehicle is supplied in the form of potential energy. More precisely, it is produced by a slight excess of ballast to permit descent. This ballast is progressively released as dredging proceeds and the excess ballast still remaining after the dredging operation is released at the end of the operation to make the machine lighter so that it can be raised again. This raising and descent can be accurately guided by the hydrodynamic form of the submarine vehicle which behaves as a "glider" under the excess apparent weight required for the descent or under the excess buoyancy required for re-ascent.
The advantage of this process is that there is a considerable energy saving in all the phases of the operation of collecting and raising the nodules. Propellers supplied with energy for travel on the sea bed are the only ones which operate for any considerable time, whilst the auxiliary manoeuvring propellers are not used very much (only for precise landing manoeuvres on the sea bed and/or for making a rendezvous when returning to the surface).
Moreover, a number of submarine machines or vehicles are known which, at shallow depths, derive their buoyancy from the leaktight seal of the hull and which, for great depths, use buoyancy products resistant to very high pressures, to constitute a "wet submarine". This vehicle comprises, in addition to the resistant sealed capsule in which the passengers are housed if the vehicle is manned, a structure forming a tubular or other form of framework connecting the various weighty parts to one another. The buoyancy product in the form of blocks of small or moderate dimensions is generally fixed to this framework. These wet submarines may or may not comprise a hydrodynamic hull which, if provided, is in the form of a thin hull, but the hull does not, under any circumstances, coincide with the outer surface of the buoyancy product. It will be appreciated that the structures described hereinbefore are a major factor in the balance sheet of apparent weight in water of the submarine machines thus formed. This consequently results in an increase in the mass of buoyancy product required to provide zero or positive buoyancy.
An example of such a vehicle is the one described and claimed in patent application No. 27 29460 filed on Sept. 30th 1977 in the name of the Applicant (U.S. Pat. No. 4,280,288).